1. Field of the Invention
The present invention relates to a printing apparatus and more particularly to a print timing control of a print head in the printing apparatus.
2. Description of the Prior Art
A variety of techniques for controlling the print timing have been known and one such example is a technology that generates a print timing by using an encoder. The encoder used by such a printing apparatus is generally known to correspond to the print resolution.
Another conventionally known example uses an encoder with a lower resolution than the print resolution of the printing apparatus, detects leading and trailing edges of two pulse signals AS and BS 90 degrees out of phase with each other and outputs a quadruple-cycle signal to generate a print timing signal with a quadruple resolution.
Still another example uses an encoder with a lower resolution than the print resolution, as in the above example, measures an interval between pulses output from the encoder, and divides the pulse interval one cycle before into n equal parts to generate a print timing signal with a resolution n times the original encoder resolution.
In the case where an encoder matching the print resolution is used, however, printing at high resolution requires an encoder that has a correspondingly high resolution, making the apparatus expensive.
Further, in the case where an encoder with a lower resolution than the print resolution is used and where the leading and trailing edges of two pulse signals AS, BS 90 degrees out of phase are detected to produce a quadruple-cycle signal and thereby generate a print timing signal with a quadruple resolution, when an optical sensor is used in the encoder, interval errors occur which include errors due to sensor characteristic of a light receiving device or the like, phase shifts between A- and B-phase signals, and errors induced by a circuit that transforms an output from the light receiving device into a rectangular pulse signal. The interval errors may cause the print timing to deviate relatively greatly from a desired position. As to a digital servo apparatus, on the other hand, Japanese Patent Laid-Open No. 7-210249 for example discloses a technique that corrects the quadruple interval errors to correct the print position represented by the quadruple signal. In the case of a printing apparatus, however, what is required is not the detection of an accurate print position corresponding to the signal but the generation of a precise print timing for a predetermined print position, and therefore what is disclosed in the official gazette cannot correct the deviation of the print position.
Further, in the case where an encoder with a lower resolution than the print resolution is used and where an interval between adjacent pulse signals is measured and the pulse signal interval one cycle before is divided into n equal parts to generate a print timing signal with a resolution n times the original encoder resolution, a time difference may occur among intervals between two adjacent pulse signals. When such a time difference occurs, a pulse signal interval in the previous cycle may extend and, to that extent, a pulse signal interval in the current cycle shorten, giving rise to a problem that a time required for data transfer and for print processing associated with head driving may become insufficient.
In any of the conventional techniques described above, sudden noise or the like can cause variations in the timing and cycle of the encoder and may result in a failure or error of the print processing.
The present invention has been accomplished to solve the above-described problems and its object is to provide a printing apparatus which, when performing a high resolution printing, can generate a precise print timing to improve the print position accuracy of a print head and thereby perform high quality printing.
Another object of the present invention is to provide a printing apparatus capable of performing printing that prevents errors associated with print positions due to disturbances such as noise from being produced.
To achieve the above objectives, a printing apparatus using a print head for printing on a print medium according to the invention comprises a head moving means for moving the print head, a head position information detection means for outputting a cyclic signal according to an amount of movement of the print head driven by the head moving means, and a phase interval detection means for measuring a time interval between predetermined reference phases of the cyclic signal output from the head position information detection means. A division means divides the time interval detected by the phase interval detection means into n equal parts and a print timing generation means generates n print timing signals, according to the time interval divided by the division means, by taking as references the predetermined reference phases associated with the time interval measurement by the phase interval detection means. A time difference detection means detects a time difference between a print end time of a previous cycle and the predetermined reference phase of a current cycle on the basis of the cyclic signal outputted from the head position information detection means and the print timing signals generated by the print timing generation means. A correction means corrects the print timing signals of a current cycle generated by the print timing generation means by an amount of the detected time difference when the print end time of the previous cycle lags the predetermined reference phase of the current cycle.
The above printing apparatus using a print head for printing on a print medium preferably has a construction in which when the print end time of the previous cycle lags the predetermined reference phase of the current cycle, the correction means delays a start timing of the current cycle print timing signal generated by the print timing generation means by an amount of the detected time difference and corrects a cycle of the current cycle print timing signal.
A printing apparatus using a print head for printing on a print medium according to the invention comprises a head moving means for moving the print head, a head position information detection means for outputting a cyclic signal according to an amount of movement of the print head driven by the head moving means, and a phase interval detection means for measuring a time interval between predetermined reference phases of the cyclic signal output from the head position information detection means. A division means divides the time interval detected by the phase interval detection means into n equal parts and a print timing generation means generates n print timing signals, according to the time interval divided by the division means, by taking as references the predetermined reference phases associated with the time interval measurement by the phase interval detection means. A correction means corrects a print timing signal of a next cycle generated by the print timing generation means according to a result of comparison between the time interval of a previous cycle and the time interval of a current cycle detected by the phase interval detection means.
The above printing apparatus using a print head for printing on a print medium preferably has a construction in which the correction means corrects a start timing and a cycle of the next cycle print timing signal generated by the print timing generation means according to a result of comparison between the previous cycle time interval and the current cycle time interval detected by the phase interval detection means.
A printing apparatus using a print head for printing on a print medium according to the invention comprises a head moving means for moving the print head, a head position information detection means for outputting a cyclic signal according to an amount of movement of the print head driven by the head moving means, and a phase interval detection means for measuring a time interval between predetermined reference phases of the cyclic signal output from the head position information detection means. A division means divides the time interval detected by the phase interval detection means into n equal parts and a print timing generation mean generates n print timing signals, according to the time interval divided by the division means, by taking as references the predetermined reference phases associated with the time interval measurement by the phase interval detection means. A correction means corrects a print timing signal generated by the print timing generation means according to a difference between the time interval detected by the phase interval detection means and a predetermined time interval when the time interval detected by the phase interval detection means is equal to or less than the predetermined time interval.
Alternatively, a printing apparatus using a print head for printing on a print medium according to the invention comprises a head moving means for moving the print head, a head position information detection means for outputting a cyclic signal according to an amount of movement of the print head driven by the head moving means, and a phase interval detection means for measuring a time interval between predetermined reference phases of the cyclic signal output from the head position information detection means. A division means divides the time interval detected by the phase interval detection means into n equal parts and a print timing generation means generates n print timing signals, according to the time interval divided by the division means, by taking as references the predetermined reference phases associated with the time interval measurement by the phase interval detection means. A correction means corrects a print timing signal generated by the print timing generation means according to a difference between the time interval detected by the phase interval detection means and a predetermined time interval when the time interval detected by the phase interval detection means is equal to or greater than the predetermined time interval.
In measuring the cycle between predetermined reference phases of the output signal of the head position information detection means such as an encoder and dividing the previous cycle into n equal parts to produce the print timing signal, when the end of the actual print processing of the previous cycle extends into the current cycle, the above construction delays the start of the print timing signal of the current cycle to that extent and shortens the current cycle according to the length of time by which the actual print processing of the previous cycle extends into the current cycle.
Because this arrangement uses the same predetermined reference phase at all times, a precise measurement of the cycle can be made even by using an encoder with not so high a precision. Further, the cycle correction can ensure error-free printing and prevent cumulative positional shifts when the end of printing extends into the next cycle.
Further, when the detected cycle is above or below a predetermined value, this is taken as being abnormal. Thus, the print timing can be generated in a cycle that falls within at least a predetermined range.
As a result, it is possible to generate a print timing with virtually high resolution at low cost and perform high quality printing with high resolution. At the same time, the print processing time can be set sufficiently large to enable efficient high-speed printing.
It is also possible to perform stable printing without error even when there are variations in the encoder outputs due to disturbances such as noise.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.